Technical aids in the diagnosis of brain death: a comparison of SEP, AEP, EEG, TCD and CT angiography

Abstract

Background: The use of technical aids to confirm brain death is a controversial matter. Angiography with the intra-arterial administration of contrast medium is the international gold standard, but it is not allowed in Germany except in cases where it provides a potential mode of treatment. The currently approved tests in Germany are recordings of somatosensory evoked potentials (SSEP), brain perfusion scintigraphy, transcranial Doppler ultrasonography (TCD), and electroencephalography (EEG). CT angiography (CTA), a promising new alternative, is being increasingly used as well.

Methods: In a prospective, single-center study that was carried out from 2008 to 2011, 71 consecutive patients in whom brain death was diagnosed on clinical grounds underwent recording of auditory evoked potentials (AEP) and SSEP as well as EEG, TCD and CTA.

Results: The validity of CTA for the confirmation of brain death was 94%; the validity of the other tests was: 94% for EEG, 92% for TCD, 82% for SSEP, and 2% for AEP. In 61 of the 71 patients (86%), the EEG, TCD and CTA findings all accorded with the clinical diagnosis. The diagnosis of brain death was established beyond doubt in all patients.

Conclusion: In this study, the technical aids yielded discordant results in 14% of cases, necessitating interpretation by an expert examiner. The perfusion tests, in particular, can give false-positive results in patients with large cranial defects, skull fractures, or cerebrospinal fluid drainage. In such cases, electrophysiologic tests or a repeated clinical examination should be performed instead. CTA is a promising, highly reliable new method for demonstrating absent intracranial blood flow. In our view, it should be incorporated into the German guidelines for the diagnosis of brain death.

Figure 1

Typical CTA findings in a brain-dead patient. CM filling stops below the base of the skull in the internal carotid artery (arrow, Figure 1a), and no filling of intracranial vessels can be seen (Figure 1b). CM filling of proximal vessel segments without signs of filling of basilar artery and terminal cortical vessels (Figure 1c). CTA, CT angiography; CM, contrast medium

Figure 2

A 71-year-old male patient after a serious road traffic accident: multiple injuries and acute subdural hematoma. Deeply unconscious with anisocoria at the scene of the accident. After admission, diagnosis was followed by craniotomy and relief of an acute subdural hematoma. The polytrauma and hyperfibrinolysis led to secondary bleeding and loss of brainstem reflexes. After onset of clinical brain death, CTA (Figure 2a) and TCD (Figure 2c) both showed residual flow. Simultaneously, SEP showed a possibly positive response over the upper cervical spine and the brainstem. Thus irreversibility could not be demonstrated at that time. EEG, however, showed no cerebral electrical activity, a finding consistent with brain death. Repeat CTA a day later (Figure 2b) showed findings consistent with brain death in all phases of the examination. CTA, CT angiography; TCD, transcranial Doppler sonography; SEP, somatosensory evoked potentials; EEG, electroencephalography